1. Field of Invention
The invention relates to a vehicular navigation system.
2. Description of Related Art
Conventionally, a variety of navigation systems have been proposed.
For example:
(1) According to a route guidance method for a vehicular navigation system disclosed in Japanese Patent Laid-Open No. Hei 7-320194, for instance, a plurality of nodes passed by a vehicle during the period from the time when a registration start key is depressed at a starting point to the time when a registration end key is depressed at a destination in an outgoing trip are stored in order in a memory device. The nodes thus passed are reversed in order, thereby forming guidance route data for a return trip. If the memory device has two nodes stored for a certain point along the outgoing route as a result of deliberate deviation therefrom, one of the two nodes is deleted. Then, a return route with no deviation is determined simply by interchanging the starting point and destination from the outgoing trip.
(2) Another conventional technology disclosed in Japanese Patent Laid-Open No. Hei 134796 relates to a route determination and display system in which a current position on a map of a vehicle or the like is displayed on a display unit, more specifically, to a system in which an outgoing route to a destination and a return route therefrom are determined and displayed. In this system, when the route determining operation is requested, the outgoing route from the starting point to the destination is determined and displayed on the map. Then, the return route is determined by interchanging the starting point and destination from the outgoing trip. The return route is displayed upon receipt of an instruction to display it.
In the above-described route guidance method (1), a plurality of nodes passed by the vehicle in the outgoing trip are registered in order, and the nodes thus registered are reversed in order to determine the return route. However, there may be a one-way road or the like where the vehicle is allowed to pass in the outgoing trip but not in the return trip. Accordingly, the vehicle may not be guided appropriately in the return trip merely by reading the nodes passed in the outgoing trip in reverse order.
Furthermore, in the case where the vehicle reaches a first-set destination with the nodes passed during the outgoing trip registered, moves around the destination without setting any specific route and returns to the starting point, the vehicle cannot be guided in the return trip unless it returns to the route whose nodes have been passed and registered during the outgoing trip.
In the above-described system (2), the destination in the outgoing trip is set as the starting point in the return trip, while the starting point in the outgoing trip is set as the destination in the return trip. Thus, the return route is determined and registered in advance. Consequently, it is unnecessary to perform any operation to determine the return route, once the vehicle has reached the destination in the outgoing trip.
However, it is to be noted herein that the return route is automatically determined once the starting point and the destination in the outgoing trip have been determined. That is, the return route is determined as an optimum route simply by interchanging the starting point and the destination in the outgoing trip without taking into consideration any specific information relating to the outgoing route. In the case where the vehicle deviates from an initially-determined route in the outgoing trip, the outgoing route is determined again automatically or by a user of the system at a point where such deviation is recognized, and the vehicle is guided along a new route, the new route is not taken into consideration at all in determining the return route.
If the user makes a trip to an unknown place to achieve a particular purpose and returns to a first starting point, it is convenient to pass the outgoing route again. This is because road conditions of the outgoing route, which has been already covered, are recognized by the user. In the case of a navigation system wherein the route to a destination is determined in advance based on a starting point or a current position of a vehicle and wherein the route guidance is given at intersections or crossroads by sound or screen display, if the system determines that the vehicle has been traveling along a wrong route, it is desirable to determine a new route from a current position of the vehicle.
In this case, it is desirable to display a key to urge the user to start the route determining operation again, so that the new route from the current position of the vehicle can be determined by depressing the key.
Furthermore, the vehicle traveling along a predetermined route may desirably take a partial detour off the original route or adopt a totally different route in response to an instruction given by the user to determine a new route.
For some reason or based on a personal preference, the user may go off the original route intentionally and instruct the system to determine or edit a different route. If the user who is familiar with an area around the starting point wants to avoid a constantly-congested trunk road along the predetermined route, for example, a new route is edited by starting the route determining operation again. The route thus edited, though different from an initially-determined optimum route, is preferred by the user. Therefore, the user requires the same route to be followed in the return trip.
However, such requirements by the user cannot be satisfied by the conventional technologies disclosed by (1) and (2).